Within the framework of the present invention, a position indication represents a current position of the aircraft, which is determined in a standard manner, with the aid of information arising from onboard positioning means which cooperate with a satellite positioning system, for example of GNSS type (“Global Navigation Satellite System”), and of inertial information generated by an onboard standard inertial system.
To guide an aircraft as precisely as possible, it is necessary to have available, in real time, a position indication which is very reliable. This will in particular be necessary for future precision aerial operations of RNP AR type (“Required Navigation Performance with Approbation Required”), on approach and at takeoff, which require that the aircraft be made to navigate inside a predetermined corridor and not to leave it. Indeed, relief or other aircraft potentially lie outside this corridor. Patent application FR-2 887 329 describes a particular display device which is suited to an operation or procedure of RNP type. According to such a procedure, the aircraft is generally guided in accordance with a predetermined flight plan, while having to comply with strict performance constraints.
Moreover, it is known that in general the operations of RNP type are operations which are carried out essentially with the aid of standard receivers associated with a Global Navigation Satellite System of GNSS type which encompasses all the existing satellite navigation systems (GPS, Galileo, etc.), with the aid of an inertial system, and with the aid of at least one flight management system for example of FMS type.
For safety reasons, one or more alarms are generally provided for, which guarantee compliance with the aforesaid performance throughout the RNP operation. When such an alarm is emitted, ability to comply with the RNP performance is lost and is announced to the pilot. Depending on the cause of the alarm, the pilot must interrupt the operation or select other onboard systems. The rest of the aerial operation is then implemented with the navigation systems still available and their residual performance.
However, to do this, these still available navigation systems use the current positions which are the cause of the alarm (in accordance with performance criteria). So, the precision and integrity associated with the current position indication that is used for the rest of the aerial operation are not controlled and do not make it possible to guarantee that the pilot can, in complete safety, interrupt the ongoing RNP operation and perform an alternative operation making it possible to extract himself from the situation in a fully reliable manner.
Consequently, it appears to be necessary to be able to monitor a current position indication, so as to be able to forewarn the pilot or onboard systems, in the event of a reliability problem. This monitoring seems particularly suited, although not exclusively, to RNP operations of aforesaid type.